Editor: ActorEditLogic: support for dynamic generation of items in dropdown

[michaeldgg2]

This PR makes it possible for EditorActorDropdown to dynamically generate items for particular actor.

This requires second constructor for EditorActorDropdown to keep backward-compatibility with existing traits (which will still use old callbacks GetLabels and GetValue).

[pchote]

IMO adding a new constructor just for downstream use isn't a great idea - it is likely to break or be removed in the future. If there's a good motivation for per-actor items then we should make the default logic use the same code paths.

[michaeldgg2]

Yes, it might seem it's somewhat specific to our mod, but this can be used any other mod. But I agree that there might be a better solution for our specific use case.

I'm reposting two more solutions from Discord here:

Another solution that I can think of is to create a completely separate IEditorActorOptions object and then widget for it - just for actor references. The trait creating IEditorActorOptions could then customize, which actors to show, or other stuff. But I believe this would be even more specific to our situation.

Yet another solution: make it possible to create entirely custom IEditorActorOptions in mod code, i.e. insert extensibility point in ActorEditLogic, which could add widgets into initContainer. This would make editor more extensible and customizable by a mod, but it would require some more work to hook it up into the infrastructure of ActorEditLogic.

[RoosterDragon]

This changes seems reasonable to me. But agree with pchote's comment. Remove the old constructor and have all existing callsites call your new, more general constructor.

[PunkPun]

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